sensors Mode-S transponder
A1F2B1
ICAO 24-bit transponder address · allocated to United States
Currently assigned to N2243U · BOEING 777-300ER · operated by UNITED AIRLINES INC
- Hex
- A1F2B1
- Octal
- 50371261
- Decimal
- 10,613,425
- Country
- US
- Tail
- N2243U
- Type
- B77W
- Flights observed
- 224
- Distinct callsigns
- 20
- Country
- US
- Last broadcast
- 2h ago
Last known position
Country allocation
The ICAO 24-bit address A1F2B1 falls within the block assigned to United States (US) by ICAO Annex 10, Volume III. Every aircraft registered in United States receives a permanent address from this block at the time of registration; the address stays with the airframe even if the aircraft is re-registered to a different operator within the country.
Callsign history 20 distinct
| Callsign | Airline | Flights | Last seen |
|---|---|---|---|
| UAL857 | - | 17 | 2026-07-13 |
| UAL862 | - | 15 | 2026-07-12 |
| UAL869 | - | 14 | 2026-06-12 |
| UAL877 | - | 12 | 2026-07-11 |
| UAL189 | - | 11 | 2026-06-28 |
| UAL1844 | - | 11 | 2026-07-10 |
| UAL872 | - | 10 | 2026-06-18 |
| UAL988 | - | 8 | 2026-06-21 |
| UAL871 | - | 8 | 2026-06-16 |
| UAL858 | - | 8 | 2026-07-14 |
| UAL40 | - | 8 | 2026-07-09 |
| UAL190 | - | 8 | 2026-06-29 |
| UAL878 | - | 7 | 2026-06-12 |
| UAL1149 | United Airlines | 7 | 2026-04-15 |
| UAL43 | - | 6 | 2026-07-09 |
| UAL42 | - | 6 | 2026-07-09 |
| UAL41 | - | 6 | 2026-07-10 |
| UAL989 | - | 5 | 2026-06-22 |
| UAL951 | United Airlines | 5 | 2026-06-22 |
| UAL950 | - | 5 | 2026-06-21 |
Recent flights last 50
| Date | Flight | Route | Takeoff | Landing | Duration |
|---|---|---|---|---|---|
| 2026-07-14 | UAL858 | - | Jul 14, 05:25 UTC | Jul 14, 07:05 UTC | 1h 40m |
| 2026-07-13 | UAL857 | - | Jul 13, 06:40 UTC | Jul 14, 06:15 UTC | 23h 35m |
| 2026-07-12 | UAL857 | SFO → PVG | Jul 12, 20:57 UTC | Jul 13, 09:02 UTC | 12h 5m |
| 2026-07-12 | UAL857 | - | Jul 12, 20:50 UTC | Jul 13, 08:15 UTC | 11h 25m |
| 2026-07-12 | UAL862 | - | Jul 12, 04:05 UTC | Jul 12, 07:45 UTC | 3h 40m |
| 2026-07-12 | UAL862 | HKG → SFO | Jul 12, 04:11 UTC | Jul 12, 16:32 UTC | 12h 21m |
| 2026-07-11 | UAL877 | SFO → HKG | Jul 11, 07:30 UTC | Jul 11, 21:03 UTC | 13h 33m |
| 2026-07-11 | UAL877 | - | Jul 11, 07:25 UTC | Jul 11, 07:50 UTC | 25m |
| 2026-07-10 | UAL1844 | EWR → SFO | Jul 10, 22:44 UTC | Jul 11, 04:24 UTC | 5h 40m |
| 2026-07-10 | UAL1844 | - | Jul 10, 22:55 UTC | Jul 11, 04:30 UTC | 5h 35m |
| 2026-07-10 | UAL41 | - | Jul 10, 09:45 UTC | Jul 10, 18:35 UTC | 8h 50m |
| 2026-07-09 | UAL40 | EWR → FCO | Jul 9, 21:48 UTC | Jul 10, 05:35 UTC | 7h 47m |
| 2026-07-09 | UAL40 | - | Jul 9, 21:50 UTC | Jul 9, 23:25 UTC | 1h 35m |
| 2026-07-09 | UAL43 | - | Jul 9, 11:00 UTC | Jul 9, 18:40 UTC | 7h 40m |
| 2026-07-09 | UAL42 | EWR → FRA | Jul 9, 01:24 UTC | Jul 9, 08:14 UTC | 6h 50m |
| 2026-07-09 | UAL42 | - | Jul 9, 01:30 UTC | Jul 9, 08:15 UTC | 6h 45m |
| 2026-07-08 | UAL78 | - | Jul 8, 10:35 UTC | Jul 8, 22:40 UTC | 12h 5m |
| 2026-07-07 | UAL837 | SFO → NRT | Jul 7, 21:55 UTC | Jul 8, 07:45 UTC | 9h 50m |
| 2026-07-07 | UAL858 | - | Jul 7, 05:15 UTC | Jul 7, 15:10 UTC | 9h 55m |
| 2026-07-06 | UAL857 | - | Jul 6, 06:20 UTC | Jul 7, 06:15 UTC | 23h 55m |
| 2026-07-05 | UAL857 | - | Jul 5, 20:50 UTC | Jul 6, 08:05 UTC | 11h 15m |
| 2026-07-05 | UAL858 | - | Jul 5, 06:45 UTC | Jul 5, 07:30 UTC | 45m |
| 2026-07-05 | UAL858 | PVG → SFO | Jul 5, 04:44 UTC | Jul 5, 15:45 UTC | 11h 1m |
| 2026-07-03 | UAL857 | SFO → PVG | Jul 3, 21:37 UTC | Jul 4, 09:51 UTC | 12h 14m |
| 2026-07-03 | UAL857 | - | Jul 3, 21:35 UTC | Jul 3, 22:00 UTC | 25m |
| 2026-07-03 | UAL862 | HKG → SFO | Jul 3, 04:45 UTC | Jul 3, 16:30 UTC | 11h 45m |
| 2026-07-03 | UAL862 | HKG → SFO | Jul 3, 04:11 UTC | Jul 3, 16:29 UTC | 12h 18m |
| 2026-07-02 | UAL877 | - | Jul 2, 07:20 UTC | Jul 2, 20:30 UTC | 13h 10m |
| 2026-06-30 | UAL810 | MNL → SFO | Jun 30, 13:58 UTC | Jul 1, 01:33 UTC | 11h 35m |
| 2026-06-30 | UAL810 | - | Jun 30, 13:55 UTC | Jul 1, 01:35 UTC | 11h 40m |
| 2026-06-29 | UAL809 | SFO → MNL | Jun 29, 21:51 UTC | Jun 30, 11:10 UTC | 13h 19m |
| 2026-06-29 | UAL809 | - | Jun 29, 22:15 UTC | Jun 30, 11:35 UTC | 13h 21m |
| 2026-06-29 | UAL190 | - | Jun 29, 01:10 UTC | Jun 29, 13:30 UTC | 12h 20m |
| 2026-06-28 | UAL189 | SFO → MNL | Jun 28, 08:19 UTC | Jun 28, 21:24 UTC | 13h 5m |
| 2026-06-28 | UAL189 | SFO → MNL | Jun 28, 08:14 UTC | Jun 28, 21:40 UTC | 13h 25m |
| 2026-06-27 | UAL1844 | EWR → SFO | Jun 27, 22:29 UTC | Jun 28, 04:05 UTC | 5h 35m |
| 2026-06-27 | UAL41 | FCO → EWR | Jun 27, 09:44 UTC | Jun 27, 18:29 UTC | 8h 45m |
| 2026-06-26 | UAL40 | - | Jun 26, 21:45 UTC | Jun 27, 05:04 UTC | 7h 20m |
| 2026-06-26 | UAL41 | FCO → EWR | Jun 26, 09:20 UTC | Jun 26, 17:59 UTC | 8h 40m |
| 2026-06-25 | UAL40 | EWR → FCO | Jun 25, 21:58 UTC | Jun 26, 05:45 UTC | 7h 47m |
| 2026-06-25 | UAL40 | - | Jun 25, 22:14 UTC | Jun 25, 23:44 UTC | 1h 30m |
| 2026-06-25 | UAL41 | FCO → EWR | Jun 25, 09:29 UTC | Jun 25, 12:04 UTC | 2h 35m |
| 2026-06-25 | UAL41 | FCO → EWR | Jun 25, 09:27 UTC | Jun 25, 18:15 UTC | 8h 48m |
| 2026-06-24 | UAL40 | EWR → FCO | Jun 24, 22:00 UTC | Jun 25, 05:35 UTC | 7h 35m |
| 2026-06-24 | UAL41 | FCO → EWR | Jun 24, 09:39 UTC | Jun 24, 18:39 UTC | 9h 0m |
| 2026-06-23 | UAL40 | EWR → FCO | Jun 23, 22:23 UTC | Jun 24, 06:31 UTC | 8h 8m |
| 2026-06-23 | UAL40 | EWR → FCO | Jun 23, 23:10 UTC | Jun 24, 06:35 UTC | 7h 25m |
| 2026-06-23 | UAL43 | - | Jun 23, 09:54 UTC | Jun 23, 17:44 UTC | 7h 50m |
| 2026-06-23 | UAL43 | FRA → EWR | Jun 23, 09:31 UTC | Jun 23, 18:00 UTC | 8h 29m |
| 2026-06-22 | UAL989 | IAD → FRA | Jun 22, 22:44 UTC | Jun 23, 05:54 UTC | 7h 10m |
About Mode-S
A Mode-S transponder code (also called an "ICAO 24-bit address" or "hex code") is a 6-character hexadecimal identifier permanently assigned to an aircraft when it's first registered. Unlike callsigns (which change with each flight) or registrations (which can change if an aircraft is sold internationally), the Mode-S address stays with the airframe for the life of the aircraft in that country.
Every ADS-B transmission from an aircraft includes its Mode-S address, making it the most reliable way to identify a specific airframe. Flight-tracking services like Apparatus use the Mode-S address as the primary key for tying position broadcasts, callsigns, and ownership records together.
Prefer a tail-number view? See the N2243U page for operator, model, and routing details .